The National Transportation Safety Board announced over the weekend that x-rays and CT scans of the lithium-ion battery pack that caught fire in a Boeing 787 Dreamliner in Boston recently was not overcharged. The battery in question powered the plane’s auxiliary power unit and the investigators have disassembled the battery and are still investigating some of the individual battery cells.

The battery fire has led airlines to stop flying the 787 planes around the world. The NTSB investigators have also said that they have examined several other components from the aircraft including battery management circuit boards and associated bundles of wire. The investigators also intend to continue testing components such as the battery charger and battery management unit.

The investigators have announced that the plane's flight data recorder indicates that the battery never exceeded its design voltage of 32 volts. The FAA issued a directive last week that the Boeing 787 Dreamliner should not fly until any problems with the battery packs are resolved.

Boeing has announced that it will halt deliveries of the 787 to customers while it works with the FAA to solve the battery issues. The batteries at the center of the investigation are lithium-ion units manufactured in Japan by GS Yusana under a subcontract to a company called Thales.

The charging current is much more important than the voltage when dealing with these types of batteries. The lower the charge current, the less likely that the battery will fail. However, Boeing must balance the charge current versus the recharge time.

The vibration environment in a modern airliner is probably less than in most other vehicles. I would say that the vibration environment of the Chevy Volt battery is worse.

But due to the energy stored in lithium batteries, a failure of one cell would certainly lead to a failure of the entire battery in short order. Perhaps the 787 needs to have the battery cells in separate cases to limit the damage if one fails.